Depends on the implementation of `@einsum`. If the macro is implemented well, that’ll actually just lower to a matrix multiplication call and you’ll have zero runtime overhead.

Otherwise, you might end up lowering to a naïve for loop which would be significantly slower. TensorCast.jl and TensorOperations.jl know how to make matrix multiplication calls but currently Einsum isn't that smart.

Macros are just syntax transformations.